In the operation of the modern internal combustion engine there are two major areas which require improvement; that is, (i) reduction of harmful contaminants, such as hydrocarbon (HC), carbon monoxide (CO) and oxides of nitrogen (NO.sub.x), in the exhaust gas emitted from the engine, and (ii) increase of the thermal efficiency of the engine.
Many methods are known for efficiently purifying harmful contaminants in exhaust gas emitted from an internal combustion engine. For example, there are known a method in which the above-mentioned three harmful contaminants (HC, CO and NO.sub.x) are simultaneously reduced by introducing a lean air-fuel mixture into the combustion engine, and a method in which a large amount of exhaust gas is recirculated into the intake system of the combustion engine so as to reduce the contaminant NO.sub.x. However, with either of these known methods there occurs a common problem in that the burning velocity of the air-fuel mixture is low and a high thermal efficiency cannot be obtained because the flame speed of such a mixture is very low. As a result, a satisfactorily high output of an engine cannot be obtained. Consequently, in the case wherein such a combustible gas mixture is used in an internal combustion engine, in order to improve the thermal efficiency of the engine, the most important factor is to increase the flame speed.
The inventors of the present invention have proposed in U.S. Pat. No. 4,191,135 which issued on Mar. 4, 1980 internal combustion engines which have combustion chambers wherein the flame speed of the combustible gas mixture can be increased.
One of the proposed engines comprises:
a cylinder block having a cylindrical bore formed therein for constituting a part of a combustion chamber in which a piston is reciprocated and a combustible mixture is burnt to generate engine power;
a cylinder head secured to the cylinder block, which head has a recess formed thereon for constituting the other part of the combustion chamber and a cavity formed therein for constituting an accumulation chamber, the accumulation chamber temporarily accumulating a part of the gas introduced into the combustion chamber; and
a valve positioned on a passage for communicating the combustion chamber with the accumulation chamber, which valve is opened approximately at the time the compression stroke of the engine is commenced and is closed approximately at the time the compression stroke is completed. The internal combustion engine according to the copending application bearing U.S. Ser. No. 969,797, now abandoned, further comprises a plurality of jets for spouting gas accumulated in the accumulation chamber, which jets are disposed in the passage communicating the accumulation chamber with the combustion chamber, whereby turbulences are generated by the gas spouted through the jets in various portions of the compressed gas within the combustion chamber. It should be noted that in these inventions the valve positioned on the passage is closed at a time which is different from the time when the valve disclosed in U.S. Pat. No. 1,648,929 is closed. It should also be noted that unburnt intake gas is accumulated within the accumulation chamber disclosed in the copending applications instead of the burnt gas disclosed in U.S. Pat. No. 1,648,929.